1. Field of the Invention
The present invention relates to a photosensitive drum assembly and a process cartridge, and more particularly, to a photosensitive drum assembly and a process cartridge having an improved structure in which a driving force transmitted from a main body of an image forming apparatus is received.
2. Description of the Related Art
Image forming apparatuses are apparatuses that print letters or images on a recording medium, such as paper, or the like. Examples of image forming apparatuses include a copy machine, a laser printer, a light emitting diode (LED) printer, a facsimile, and the like.
Generally, image forming apparatuses include a cartridge that includes toner and records letters or images to be printed on a recording medium, such as paper, or the like. The cartridge is generally attached to or detached from the image forming apparatus so as to replace toner.
FIG. 1 is a schematic view of a structure of an image forming apparatus according to the related art, FIG. 2 is a perspective view of an appearance of a process cartridge 2 of the image forming apparatus illustrated in FIG. 1, and FIG. 3 is a cross-sectional view of a photosensitive drum 110 of the process cartridge 2 of FIG. 1 and peripheral elements of the process cartridge 2.
Referring to FIGS. 1 and 2, the image forming apparatus according to the related art may include the process cartridge 2 that stores toner and supplies the toner to a recording medium 88. The image forming apparatus enables a plurality of rollers 73, 74, 75, 76, and 77 installed at a main body 1 of the image forming apparatus to rotate, supplies the recording medium 88, such as paper, or the like, to a direction indicated by reference numeral 88s, simultaneously transmits data, such as an image to be printed, or the like, to the process cartridge 2, and transfers a predetermined amount of the toner stored in a toner storing container 28 onto the recording medium 88 via a photosensitive drum 110 installed at the process cartridge 2, thereby printing a desired image on the recoding medium 88.
To this end, the process cartridge 2 may include the photosensitive drum 110, a cleaning unit, a exposure unit, a developing unit, and the like. The process cartridge 2 may operate in such a way that, if charges are accumulated on the photosensitive drum 110, photosensitization occurs in the photosensitive drum 110, the toner is fused on a photosensitized portion of the photosensitive drum 110, is transferred onto the recording medium 88 and is fixed on the recording medium 88 by heating the toner.
The process cartridge 2 is provided to be attached to or detached from the main body 1 of the image forming apparatus, and a drive assembly 20 that is combined with the photosensitive drum 110 when the process cartridge 2 is mounted on the main body 1, is combined with a driving force providing unit provided to the main body 1 so as to receive a rotation driving force. In detail, a protrusion 21 protrudes from an end of the drive assembly 20 so as to receive a rotation force. The protrusion 21 may be combined with elements of the main body 1.
Unexplained reference numeral 49 denotes the case that supports rotation of the photosensitive drum 110 of the process cartridge 2, unexplained reference numeral 30g denotes a gear for transmitting a rotation force and that is disposed at an opposite side to the drive assembly 20, unexplained reference numeral 22 denotes a support that protrudes from the drive assembly 20, and unexplained reference numeral 23 denotes a gear formed on an outer circumferential surface of the drive assembly 20.
FIG. 4 is a perspective view of a rotation driving force transmitting structure of an image forming apparatus according to the related art, and FIG. 5 is a cross-sectional view of FIG. 4. In detail, FIGS. 4 and 5 illustrate a rotation driving force transmitting structure of an image forming apparatus that transmits a driving force by using the above-described method and that is disclosed in Korean Patent Registration No. 0258609.
Referring to FIGS. 4 and 5, when a process cartridge 2 is inserted in a main body 1 of the image forming apparatus, a twisted protrusion 21 of a drive assembly 20 that is combined with one side of a photosensitive drum 110 disposed on the process cartridge 2, is inserted in a twisted hole 181 of a driving shaft 180 disposed on the main body 1 of the image forming apparatus. As the driving shaft 180 is rotated by a driving motor installed in the main body 1 of the image forming apparatus, the twisted hole 181 of the driving shaft 180 and the twisted protrusion 21 are combined with each other and are rotated so that a driving force provided by the driving motor may be transmitted to the photosensitive drum 110 and the photosensitive drum 110 may also be rotated.
In this case, the twisted protrusion 21 is in point contact with three parts of an inner side surface of the twisted hole 181 based on a cross-section of the twisted protrusion 21. The twisted protrusion 21 as a whole is in line contact with three parts of the inner side surface of the twisted hole 181, and thus the driving force is transmitted to the twisted protrusion 21.
The driving shaft 180 may include a gear portion 181g to which the driving force is transmitted from the driving motor.
However, the above-described related art has the following problems.
Since the driving force is transmitted to the twisted protrusion 21 based on the cross-section of the twisted protrusion 21 due to point contact, stress is concentrated on a small contact point, the speed of abrasion increases, the contact point is easily worn or damaged, and there is a limitation in performing precise performance during an expected life span of the process cartridge 2.
In detail, in a twisted combination coupling disclosed in Korean Patent Registration No. 0258609, since the twisted protrusion 21 has a complementary shape to the twisted hole 181 and a smaller size than that of the twisted hole 181, a gap is formed between the twisted protrusion 21 and the twisted hole 181 in an angular direction. Thus, when the driving force is transmitted to the twisted protrusion 21, a corner of the twisted protrusion 21 is pressed by the driving force and is closely adhered to one of two side surfaces that constitute one of a plurality of corners of the twisted hole 181 and thus the corner of the twisted protrusion 21 is in point contact with the twisted hole 181. However, when the driving force is not transmitted to the twisted protrusion 21, since the driving force that enables a corner of the twisted protrusion 21 to be pressed and closely adhered to one of two side surfaces of the twisted hole 181 does not exist, the point contact between the twisted protrusion 21 and the twisted hole 181 is released. Since several thousands or several ten thousands times of printing operations are attempted during a life span of the process cartridge 2, a large concentrative load is repeatedly applied to or removed from a local part in which point contact between the twisted protrusion 21 and the twisted hole 181 occurs. Thus, even when a surface pressure that is generated in the point contact portion, does not affect the limit of resisting pressures of materials used in forming the twisted protrusion 21 and the twisted hole 181, a fatigue destruction phenomenon occurs in the point contact portion. In particular, due to the driving force applied to the twisted protrusion 21 in a state where the gap is formed between the twisted protrusion 21 and the twisted hole 181, the instant the corner of the twisted protrusion 21 is rapidly changed into be in point contact with the inner side surface of the twisted hole 181, collision occurs in an area where point contact occurs. Thus, the fatigue destruction phenomenon is accelerated due to this collision.
In addition, when the twisted hole 181 is rotated and is changed from a driving force non-transmission state to a driving force transmission state, first, the corner of the twisted protrusion 21 is in contact with the inner side surface of the twisted hole 181. After the contact has occurred, the twisted hole 181 is further rotated relative to the twisted protrusion 21 and thus the twisted protrusion 21 is pulled out in an axial direction, and if the twisted protrusion 21 is completely pulled out in the axial direction and an axial position of the twisted protrusion 21 is fixed, a series of operations of performing twisted combination between the twisted hole 181 and the twisted protrusion 21 are performed. In this case, a large concentrative load is applied to a local part of the point contact portion of the twisted protrusion 21 and the twisted hole 181, and the point contact portion is moved by friction and thus, abrasion of the point contact portion is very large.
In this way, if the point contact portion between the twisted protrusion 21 and the twisted hole 181 is worn or damaged, a concentric state of the driving shaft 180 and the photosensitive drum 110 cannot be kept, and shake occurs, and when the photosensitive drum 110 is rotated, rotation precision is lowered, and the quality of an image is lowered.